Gonadal Development: Testes and Ovaries

• Embryology involves the development of an embryo from fertilization to the fetus stage.
• The intermediate mesoderm condenses to form the urogenital ridge.
• Primordial germ cells (PGCs) from the yolk sac migrate toward the gut tube and infiltrate the gonads.
• Gonads develop from the urogenital ridge.
• Gonads develop into either ovaries or testes.
• The ductal system is also derived from the urogenital ridge.

Gonadal Development: Testes

• XY chromosomes result in medulla development.
• SRY gene presence leads to the production of Testis Determining Factor (TDF).
• TDF causes the gonads to develop into testes.
• Testes produce testosterone and Mullerian Inhibiting Factor (MIF).
• Testosterone stimulates growth of mesonephric ducts.
• Mesonephric ducts develop into: Ducts, epididymis, Vas deferens, Seminal vesicles, and Ejaculatory duct.
• Sertoli cells produce Mullerian Inhibiting Factor (MIF).

Gonadal Development: Ovaries

• XX chromosomes result in cortex development.
• Lack of SRY gene, therefore no TDF.
• Absence of TDF results in the gonads developing into ovaries.
• Ovaries produce oocytes that mature into follicular cells that produce estrogen.
• No testes are formed
• Absence of sertoli cells, therefore no MIF is produced.
• The absence of MIF stimulates the formation of the Mullerian duct.
• Mullerian ducts develop into: Fallopian tubes, uterus, and the upper 2/3 of the vagina.

External Genitalia Development

• Sexually indifferent stage.
• Male external genitalia, DHT stimulates the formation of Glans penis, Corpus spongiosum, and Corpus cavernosum.
• Male external genitalia, the genital tubercle forms the glans penis.
• Male external genitalia, the labioscrotal sinus forms the scrotum.
• Male external genitalia, the urethral folds form the body of the penis and penile urethra.
• Female external genitalia, estrogen stimulates the formation of the clitoris and vestibular bulbs.
• Female external genitalia, the genital tubercle forms the clitoris + vestibular bulbs.
• Female external genitalia, the labioscrotal sinus forms the labia majora.
• Female external genitalia, the urethral folds form the labia minora.

Gubernaculum

• In males, it guides the descent of the testes into the scrotum.
• In females, it guides the descent of the ovaries into the pelvis.
  • Caudal part: Forms the ovarian ligament (between the ovary and uterus).
  • Forms the round ligament (connects from the uterus to the labia).
  • Cranial part, also referred to as the suspensory ligament.